Electric arc furnace dust as coating material for iron ore pellets for use in direct reduction processes

ABSTRACT

Disclosed are coating compositions and methods for their use, comprising 90 wt. % electric arc furnace dust based on the total dry weight of the coating composition. The electric arc furnace dust includes at least 40 wt. % of Fe 2 O 3  and at least 30 wt. % of CaO and CaCO 3  combined, based on the total dry weight of the electric arc furnace dust.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/245,760, filed Oct. 23, 2015, and U.S. Provisional Application No.62/245,759, filed Oct. 23, 2015. The contents of the referencedapplications are incorporated into the present application by reference.

BACKGROUND OF THE DISCLOSURE A. Technical Field

The present disclosure relates to coating compositions for iron orepellets comprising electric arc furnace dust. Also disclosed are ironore pellets comprising a first coating and a second coating comprisingelectric arc furnace dust, a process of manufacturing the iron orepellets, and a process of reducing the iron ore pellets to form reducediron pellets with reduced agglomeration of the iron ore pellets.

B. Description of the Related Art

Direct reduction (DR) of iron ores is a fundamental step in commercialmanufacture of iron. Several direct reduction processes, including thoseusing fine ore, lump ore and pellets, have been developed. Someprocesses use natural gas as fuel reductant, whereas others are based oncoal. Approximately 90% of directly reduced iron (DRI) in the world isproduced by gas-based vertical shaft furnace processes owing to theirlow energy consumption and high productivity. Two of the common verticalshaft furnace processes are the Midrex (USA) and Tenova HYL (Mexico)processes, both of which use pellets and/or lumps of iron ore as feedstock.

The direct reduced iron (DRI) productivity is dependent on severalfactors including the iron ore pellet reduction properties, the reducinggasses concentration and the reaction temperature. Higher temperature,in general leads to higher productivity or faster reduction of thepellets but is limited by the sticking tendency of the pellets at hightemperatures which leads to cluster formation and an uneven flow of orepellets and gases. One drawback encountered with gaseous shaft furnacesis sticking or agglomerating of iron ore pellets. This unintendedagglomeration of pellets can make continuous operation difficult. Inmoving-bed shaft reduction processes, such as Midrex and HYL III, theavoidance of sticking is essential. The sticking tendency imposes anupper limit on the reduction temperature and, hence, on the productivityof the reduction process.

In direct reduction processes the product is freshly reduced iron in asolid state. Therefore, it is crucial for the material flow in thereducing module that the solid product does not agglomerate or formaggregates that block the material flow within and out of the reactor[Direct reduced iron: Technology and Economics of Production and Use,ed. by J. Feinman and D. R. Mac Rae, ISS, Warrendale, Pa.,(1999).—incorporated herein by reference in its entirety]. If thepellets have little or no tendency to stick then the reductiontemperature and therefore throughput can be increased. An increase of100° C. in the reduction temperature can significantly increasethroughput [Wong P L M, Kim M J, Kim H S, Choi C H. IronmakingSteelmaking, 1999: 26: 53-57.—incorporated herein by reference in itsentirety]. High reduction temperature also minimizes degradation andre-oxidation of the reduced product.

Previous methods to prevent and/or lessen the tendency for agglomerationand sticking of iron ore pellets have included lower temperatures,higher basicity, and changes in gangue content. However, decreasing thereducing temperature of the DRI process to avoid this problem can causea significant drop in throughput. As an example, a decrease from 850° C.to 750° C. can result in a decrease of 30-40% in throughput [L. G.Henderickson and J. A. Sandoval: Iron Steel Soc. AIME, 1980,35-48.—incorporated herein by reference in its entirety]. High basicityand gangue content may also result in larger slag volume and less metalthroughput leading to unfavorable economic and operation conditions.

One way to prevent pellet agglomeration is to coat the iron surfaceswith a coating material that is inactive under the reducing conditionsin the shaft furnace. However, a single coating has drawbacks such asineffective agglomerate prevention during reduction and the loss of thecoating prematurely during shipment or movement prior to reduction[Jerker Sterneland and Par G. Jonsson ISIJ International, Vol. 43(2003), No. 1, pp. 26-35; and Cano JAM, Wendling F. Mining Eng 1993: 45:633-636; and Jianhua Shao, Zhancheng Guo, and Huiqing Tang, Steelresearch int., 84 (2013) No. 2, 111-118. —each incorporated herein byreference in its entirety]. For this reason, the iron ore pellets areoften coated with materials to minimize adhesion tendencies. Usuallythese materials are sprayed in solution form so that a thin layer isformed and bonded with the surface of the pellets which then acts as abarrier between the surface of adjacent pellets during high temperatureexposure, thus allowing for more free movement of the pellets duringdownward movement in the shaft and at the same time allowing for moreuniform upward flow of the reducing gases during reduction processes.The suitability or effectivity of the coating is dependent on itsability to adhere with the pellet surface to such an extent that it isnot removed during shipment, movement on a conveyor belt or charginghopper as well as inside the shaft while rolling downwards and rubbingwith each other.

In the production of steel, large amounts of material are consumed, butonly a fraction is incorporated into the final product. For example,integrated mills use 2.4 tons of iron ore and other inputs for each tonof crude steel produced. This waste carries an economic andenvironmental impact. All steel production processes form wastematerials that contain oxidized iron and other oxidized metals such ascalcium, zinc, magnesium, silicon, lead, chromium, and cadmium. Thiswaste material is usually in form of dust in the gas waste streams, thegases are filtered and the dust is collected in bag houses. For example,during the electric arc furnace process, the high temperatures requiredto melt the feed material produce a byproduct referred to as electricarc furnace (EAF) dust. This dust is difficult to process because of itsfine particle size and despite its substantial metal content isessentially worthless.

The Environmental Protection Agency classifies this EAF dust as ahazardous waste due to the presence of toxic oxides. Accordingly, itsdisposal has become a major problem for steel producers. Significanteffort has been focused on developing an economical treatment processfor EAF dust that renders it nonionic or nontoxic by removing the toxicheavy metals or by immobilizing the toxic materials in a stabilizedcomposition for disposal or as a recycled product. These processes arenot economical and the toxicity of their products is unclear. Thus, aneed exists to reclaim and/or repurpose EAF dust in a cost-effective andenvironmentally safe way.

BRIEF SUMMARY OF THE DISCLOSURE

In view of the forgoing, one aspect of the present disclosure is toprovide coating compositions comprising electric arc furnace dust thatallow for the utilization of a waste material and provide sustainabilityand cost saving measures in steel plant operation. A second aspect ofthe present disclosure is to provide iron ore pellets comprising an ironore core that is coated with a first coating and a second coatingcomprising the coating composition that reclaims waste electric arcfurnace dust. A third aspect of the present disclosure is a process formanufacturing the iron ore pellets. A fourth aspect of the presentdisclosure is a process for reducing the iron ore pellets at hightemperature and throughput with reduced agglomeration to efficiently andeconomically form reduced iron.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of the reduction under load apparatus.

FIG. 2A is a schematic diagram of the tumble drum apparatus in frontview.

FIG. 2B is a schematic diagram of the tumble drum apparatus in sideview.

FIG. 3 is an X-ray diffraction (XRD) analysis of iron ore pellets.

FIG. 4A is a scanning electron microscope (SEM) micrograph of iron orepellets.

FIG. 4B is a SEM micrograph of iron ore pellets.

FIG. 5 is a SEM photo of electric arc furnace dust.

FIG. 6 is an energy-dispersive X-ray spectroscopy (EDX) analysis ofelectric arc furnace dust.

FIG. 7 is a SEM photo of the electric arc furnace dust coating layer ofiron ore pellets.

FIG. 8 is an EDX analysis of the electric arc furnace dust coating layerof iron ore pellets.

FIG. 9 is a SEM photo of the electric arc furnace dust coating layer ofiron ore pellets after a rubbing test.

FIG. 10 is an EDX analysis of the electric arc furnace dust coatinglayer of iron ore pellets after a rubbing test.

FIG. 11 is a SEM photo of the cement coating layer of iron ore pellets.

FIG. 12 is an EDX analysis of the cement coating layer of iron orepellets.

FIG. 13 is a SEM photo of the cement coating layer of iron ore pelletsafter a rubbing test.

FIG. 14 is an EDX analysis of the cement coating layer of iron orepellets after a rubbing test.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

According to a first aspect, the present disclosure relates to a coatingcomposition comprising electric arc furnace dust in an amount of atleast 90% based on the total dry weight of the coating composition.

Electric arc furnace (EAF) dust, or lime dust, is the solid materialrecovered from the off-gases from the production of molten steel and/oriron including electric arc furnaces. An electric arc furnace is afurnace that heats charged material by means of an electric arc. Itallows steel to be made from 100% scrap metal feedstock. EAF dust isgenerated during the melting of materials in an electric arc furnace andcollected by a de-dusting system such as bag filters or electrostaticprecipitators and stored. Generally, the EAF dust is a complex materialcomprising small fines of mostly metal oxides. The predominant materialis iron oxide with the remainder comprising oxides of calcium, zinc,chromium, lead, magnesium, manganese, sodium, nickel, and/or potassium.The composition of the dust is directly associated with the chemistry ofthe metallic charge used in the electric arc furnace. For example,processes that recycle scrap metal from sources as varied asautomobiles, railroad rails or discarded structural steel generate EAFdust with larger proportions of zinc, iron and lead and smallerproportions of tin, cadmium, chromium, copper, silica, lime, and/oralumina.

In one embodiment, the coating composition and the electric arc furnacedust substantially comprises Fe₂O₃, CaO, and CaCO₃. In a preferredembodiment, other materials are present in less than 10 wt. %,preferably less than 5 wt. %, preferably less than 3 wt. %, preferablyless than 2 wt. %, preferably less than 1 wt. %, preferably less than0.5 wt. % relative to the total weight of the coating composition andthe electric arc furnace dust.

In one embodiment, the electric arc furnace dust comprises greater than40 wt. % of Fe₂O₃, preferably greater than 45%, preferably greater than50%, preferably greater than 55%, preferably greater than 60%,preferably greater than 65%, preferably greater than 66%, preferablygreater than 67%, preferably greater than 68%, preferably greater than69 wt. % of Fe₂O₃ relative to the total weight of the electric arcfurnace dust. The Fe₂O₃ present in the electric arc furnace dust isconsistent with the description of Fe₂O₃ in the iron ore core providedherein below. In another preferred aspect, the electric arc furnace dustcomprises 45 wt. % to 60 wt. % Fe₂O₃ or 50 wt. % to 55 wt. % Fe₂O₃ basedon the total weight of the dust.

The coating composition preferably comprises at least 90% by weight ofelectric arc furnace dust. Preferably the coating composition comprisesat least 95% by weight, at least 96% by weight, at least 97% by weight,at least 98% by weight, at least 99% by weight of electric arc furnacedust. The coating composition preferably consists of electric arcfurnace dust.

“Slag” as used herein, refers to the by-product left over after adesired metal has been separated (i.e., smelted) from its raw ore. Slagis usually a mixture of metal oxides and silicon dioxide. However, slagscan contain metal sulfides and elemental metals. While slags aregenerally used to remove waste in metal smelting, they can also assistin the temperature control of the smelting and minimize any re-oxidationof the final liquid metal product before the molten metal is removedfrom the furnace and used to make solid metal.

In one embodiment, steel production involves an oxidation process wherelime is used to form a liquid slag which absorbs impurities from theliquid metal through formation of complex oxides in the liquid slag.Oxidation is simply the addition of oxygen into the furnace, causingmetals and non-metallics to form oxides that are lighter than the liquidsteel and as such float to the surface of the bath. As some metallicoxides are acidic in nature, they can react with the basic refractoriesof the furnace. A basic slag is made using lime and dolomitic lime whichprotects the furnace refractory. Basic slag practice is utilized formost grades of steel. Electric arc furnace dust, or lime dust, isgenerated during steel making operations in an electric arc furnacewhere the charging of lime is used towards the formation of “slag.” Theamount of lime addition is based on the silicon and aluminum levels ofthe steel bath and can affect the composition of the electric arcfurnace dust.

Lime is calcium-containing inorganic material in which carbonates,oxides, and hydroxides predominate. Lime may refer to quicklime or burntlime, which is calcium oxide that has been derived from calcininglimestone. Lime may also refer to hydrated lime or slaked lime, which iscalcium hydroxide which has been derived from the hydration ofquicklime. Therefore, “lime” as used herein, may refer to calciumcarbonate, calcium oxide or calcium hydroxide containing materialsincluding, but not limited to, dololime, lump lime or special lime, andmixtures thereof.

In one embodiment, the coating composition and the electric arc furnacedust comprise greater than 30 wt. % of CaO and CaCO₃ combined,preferably greater than 35%, preferably greater than 40%, preferablygreater than 45%, preferably greater than 50%, preferably greater than55%, preferably greater than 56%, preferably greater than 57%,preferably greater than 58%, preferably greater than 59 wt. % of CaO andCaCO₃ combined relative to the total weight of the electric arc furnacedust. In another preferred embodiment, the electric arc furnace dustcomprises 20 wt. % to 30 wt. % CaCO₃ and 10 wt. % to 20 wt. % CaO,preferably 23 wt. % to 27 wt. % CaCO₃ and 12 wt. % to 17 wt. % CaO.

In another embodiment, the electric arc furnace dust comprises lime asdescribed above. In one embodiment, the coating composition and electricarc furnace dust comprises primarily Fe₂O₃, CaO, and CaCO₃, and portionsof MgO and SiO₂.

Magnesium oxide or magnesia is a white hygroscopic solid mineral thatoccurs naturally as periclase. It consists of a lattice of Mg²⁺ ions andO²⁻ ions held together by ionic binding. In one embodiment, the coatingcomposition comprises electric arc furnace dust and the electric arcfurnace dust and coating composition comprise less than 5 wt. % of MgO,preferably less than 4%, preferably less than 3%, preferably less than2%, preferably less than 1 wt. % of MgO relative to the total weight ofthe electric arc furnace dust.

Silicon dioxide or silica is an oxide of silicon most commonly found innature as quartz. Silica is one of the most complex and most abundantfamilies of materials existing both as several minerals and synthetics.Examples include fused quartz, crystal, fumed silica, silica gel andaerogels. In one embodiment, the coating composition comprises electricarc furnace dust and the coating composition and electric arc furnacedust comprise less than 5 wt. % of SiO₂, preferably less than 4%,preferably less than 3%, preferably less than 2%, preferably less than 1wt. % of SiO₂ relative to the total weight of the electric arc furnacedust.

In one embodiment, the coating composition comprises electric arcfurnace dust and the coating composition and electric arc furnace dustare substantially free of zinc, chromium, manganese, lead, nickel,sodium, and/or potassium. These compounds are generally present in lessthan 1 wt. %, preferably less than 0.5 wt. %, preferably less than 0.1wt. %, preferably less than 0.01 wt. %, preferably less than 0.001 wt. %relative to the total weight of the electric arc furnace dust.

Other inorganic compounds may be present in the electric arc furnacedust and coating composition including, but not limited to, aluminum asAl₂O₃, antimony, arsenic, barium, boron, copper, mercury, selenium,silver, molybdenum, thorium, uranium, vanadium, strontium, cadmium,lithium, sulphate or chloride, and oxides and mixtures thereof. Thesecompounds are generally present in less than 0.5 wt. % or even 0 wt. %relative to the total weight % of the electric arc furnace dust.

In one embodiment, the coating composition comprising electric arcfurnace dust is substantially free of reducing agents including, but notlimited to, ferrous chloride and/or ferrous sulfate. These agents aresometimes used to solidify the electric arc furnace dust before, during,or after storage. In another embodiment, the coating composition mayfurther comprise a binder material. The “binder” material refers to anymaterial or substance that holds or draws other materials together toform a cohesive whole mechanically, chemically or as an adhesive. In apreferred embodiment, the binder material may refer to any portion ofthe coating composition that can harden or solidify onto the particlesof the coating composition holding the coating mixture in place on anysurface. In a preferred embodiment, the binding material is at least oneselected from the group consisting of a cement material including, butnot limited to, non-hydraulic cements, hydraulic cements, Portlandcement, Portland cement blends (i.e., Portland blast furnace slagcement, Portland fly ash cement, Portland pozzolan cement, Portlandsilica fume cement, masonry cements, expansive cements, white blendedcements, colored cements, very finely ground cements), other cements(i.e., pozzolan-lime cements, slag-lime cements, supersulfated cements,calcium sulfoaluminate cements, “natural” cements, geopolymer cements)and mixtures thereof and a clay material including, but not limited to,kaolinites, montmorillonite-smectites, illites, chlorites, and mixturesthereof. A further detailed exemplary chemical analysis of electric arcfurnace dust that may be used as the coating composition is shown inTable 2.

It is envisioned that other types of metallurgic dusts may be used inlieu of electric arc furnace dust or as a further portion of the coatingcomposition including, but not limited to, iron scrap, iron rougerecovered from steel cleaning lines, mill scale, iron containingminerals and low grade iron based pigments and other solids recoveredfrom electric arc furnaces, basic oxygen furnaces, and blast furnaces.As used herein, “metallurgic dust” refers to any unpurified metalcomposition comprising a significant portion of iron compositions.

In one embodiment, the coating composition is substantially granular andcomprises grains with an average particle size of 1-20 μm, preferably1-15 μm, more preferably 2-10 μm. It is additionally envisaged that thecoating composition may comprise some coarse grains with an averageparticle size of 1-10 mm. In a preferred embodiment, these coarse grainscomprise less than 10 wt. %, preferably less than 5 wt. %, preferablyless than 4 wt. %, preferably less than 3 wt. %, preferably less than 2wt. %, preferably less than 1 wt. % of the coating composition by weightrelative to the total weight of the coating composition. In a preferredembodiment, the coating composition is a dry powdered material. Thecoating composition is equally envisaged as a slurry, solution,suspension, dispersion, and/or emulsion. In one embodiment, the slurrycomprises 10-30 wt. %, preferably 15-25 wt. %, preferably 18-22 wt. % ofthe coating composition relative to the total weight of the slurry. Theweight percentages described above generally refer to dry weights of thecoating composition.

According to a second aspect, the present disclosure relates to iron orepellets including an iron ore core. Iron ores are rocks and mineralsfrom which metallic iron can be economically extracted. The ores aretypically rich in iron oxides and vary in color from dark grey, brightyellow, deep purple to rusty red. The iron itself is usually found inthe form of magnetite (Fe₃O₄, 72.4% Fe), hematite (Fe₂O₃, 69.9% Fe),goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH).n(H2O)) or siderite(FeCO₃, 48.2% Fe) and mixtures thereof. Ores containing very highquantities of hematite or magnetite (greater than ˜60% iron) are knownas natural ore or direct shipping ore. These ores can be fed directlyinto iron-making blast furnaces. Iron ore is the raw material used tomake pig iron, which is one of the main raw materials to make steel.

Iron (III) oxide or ferric oxide is the inorganic compound with formulaFe₂O₃. It is one of the three main oxides of iron, the other two beingiron (II) oxide (FeO) which is rare, and iron (II, III) oxide (Fe₃O₄)which also occurs naturally as the mineral magnetite. As the mineralknown as hematite, Fe₂O₃ is the main source of iron for the steelindustry. Fe₂O₃ is ferromagnetic, dark red, and readily attacked byacids.

Fe₂O₃ can be obtained in various polymorphs. In the major polymorphs, αand γ, iron adopts an octahedral coordination geometry, each Fe centeris bound to six oxygen ligands. α-Fe₂O₃ has the rhombohedral corundum(α-Al₂O₃) structure and is the most common form. It occurs naturally asthe mineral hematite which is mined as the main ore of iron. γ-Fe₂O₃ hasa cubic structure, is metastable and converted to the alpha phase athigh temperatures. It is also ferromagnetic. Several other phases havebeen identified, including the β-phase, which is cubic body centered,metastable, and at temperatures above 500° C. converts to alpha phase,and the epsilon phase, which is rhombic, and shows propertiesintermediate between alpha and gamma phase. This phase is alsometastable, transforming to the alpha phase between 500 and 750° C.Additionally, at high pressure an iron oxide can exist in an amorphousform. The ore in the iron ore core may have an α polymorph, a βpolymorph, a γ polymorph, an ε polymorph or mixtures thereof.

The iron (III) oxide in the iron ore core may also be in the form of aniron hydrate. When alkali is added to solutions of soluble Fe(III) saltsa red-brown gelatinous precipitate forms which is Fe₂O₃.H₂O (alsowritten as Fe(O)OH). Several forms of the hydrate oxide of Fe(III) existas well.

The term “iron ore core” as used herein refers to an iron rich material(i.e., greater than 40 wt. %, preferably greater than 50 wt. %, morepreferably greater than 60 wt. % elemental iron by weight), onto which asingle or a plurality of coatings are added to form a surface coatediron ore core.

The iron ore core may be a porous starting material that becomes coated,and the interface between the iron ore core and the coating material mayalso form pores. In this disclosure, “porosity” is an index showing aratio of void volume with respect to an entire volume of a structure(e.g., the iron ore core, the first coating, the second coating). Theporosity can be calculated, for example, by taking a photograph of thecross sectional structure, measuring a total void area using thephotograph, and calculating the porosity as a ratio of void area withrespect to an entire cross sectional area of the structure. In oneembodiment, the iron ore core has a porosity of 1-40%, preferably 5-35%,more preferably 10-30%.

In the present disclosure, the general shape and size of the iron orecore may dictate the shape and size of the iron ore pellets describedherein. In a preferred embodiment, the iron ore cores of the presentdisclosure are in the form of a pellet, which is spherical orsubstantially spherical (e.g., oval, oblong, etc.) in shape. However,the iron ore cores disclosed herein may have various shapes other thanspheres. For instance, it is envisaged that iron ore cores may be in theshape of a “lump” or a “briquette.” Lumps or briquettes tend to have amore cubical or rectangular shape when compared to pellet forms.Therefore, the iron ore cores of the present disclosure may also begenerally spherical, cubic, or rectangular in shape. The size of theiron ore core may also dictate the size of the iron ore pellets herein.In one embodiment, the iron ore core has an average diameter of 5-20 mm,preferably 8-18 mm, more preferably 10-16 mm, although the size may varyfrom these ranges and still provide acceptable iron ore pellets.

In addition to iron and/or iron oxide, various non-ferrous materials(i.e., metals and non-metals) may be present in the iron ore coreincluding, but not limited to, aluminum, copper, lead, nickel, tin,titanium, zinc, bronze, metal oxides thereof, metal sulfides thereof,calcium oxide, magnesium oxide, magnesite, dolomite, aluminum oxide,manganese oxide, silica, sulfur, phosphorous, and combinations thereof.The total weight % of these non-ferrous materials relative to the totalwt. % of the iron ore core is typically no more than 40%, preferably nomore than 30%, preferably no more than 20%, preferably no more than 15%,preferably no more than 10%, preferably no more than 5%, preferably nomore than 4%, preferably no more than 3%, preferably no more than 2%,more preferably no more than 1%.

The conventional route for making steel includes using one or moresintering or pelletization plants, coke ovens, blast furnaces, and basicoxygen furnaces. Such plants require high capital investment and rawmaterials of stringent specifications. Direct reduction, an alternativeroute of iron making, has been developed to overcome some of thesedifficulties of conventional blast furnaces. Iron ore is reduced insolid state to form direct reduced iron (DRI). The most importantreaction of iron (III) oxide is its carbothermal reduction, which givesiron used in steel-making (formula I):

Fe₂O₃+3CO→2Fe+3CO₂  (I):

The investment and operating costs of direct reduction plants are lowcompared to integrated steel plants. As used herein, direct-reduced iron(DRI), also known as sponge iron, is produced from the direct reductionof iron ore in the form of lumps, pellets, or fines by a reducing gasproduced from natural gas or coal. The reducing gas is a mixture, themajority of which is hydrogen (H₂) and carbon monoxide (CO) which act asreducing agents. Direct reduced iron has about the same iron content aspig iron, typically 90-94%.

The direct reduction of iron ore pellets at high temperature (e.g.,greater than 400° C.) may lead to the formation of agglomerates. As usedherein, the term “agglomerates” or “agglomerated” refers to two or moreiron ore pellets, either coated (i.e., a first coating, a secondcoating, or both) or non-coated (i.e., the iron ore core itself), whichare attached to form a pellet cluster that has a longest length of atleast 25 mm in any measurable direction. For spherical or substantiallyspherical pellet agglomerates, longest length refers to the longestlinear diameter of the pellet agglomerate. For non-spherical pelletagglomerates, such as pellet agglomerates that form a cubic shape, thelongest length may refer to any of the length, width, or height of theagglomerate. The iron ore pellets may be attached to each other in anyreasonable manner, including attached through surface coatinginteractions (e.g., glued, tacked, cemented, pasted, etc.), attached byhighly connected or integral interactions (e.g., melted together, fused,amalgamated, etc.), or entrapped within a cluster (e.g., sandwichedbetween a plurality of attached pellets). The iron ore pellets may alsobe attached as a result of interlocking fibrous iron precipitates (ironwhiskers). For instance, growth of iron whiskers may lead to pelletsthat are hooked or entangled to each other through the fibrous ironwhiskers. Therefore, one object of the present disclosure is to providea coating for iron ore that prevents the formation of agglomeratesbefore, during and/or after direct reduction processes.

The iron ore pellets of the present disclosure also include a firstcoating comprising at least one selected from the group consisting ofbauxite, bentonite, and dolomite. The iron ore core coated with a firstcoating is referred to herein as a “coated iron core” or “coated core.”

Bauxite is an aluminum ore and the predominant source of aluminumthroughout the world. It consists mostly of the minerals gibbsiteAl(OH)₃, boehmite γ-AlO(OH), and diaspore α-AlO(OH), mixed with the twoiron oxides goethite FeO(OH) and hematite (Fe₂O₃), the clay mineralkaolinite Al₂Si₂O₅(OH)₄, and small amounts of anatase TiO₂. Lateriticbauxites (silicate bauxites) are distinguished from karst bauxite ores(carbonate bauxites). In one embodiment, the first coating comprisesbauxite and the bauxite first coating comprises 40-60% Al₂O₃, 10-30%Fe₂O₃, 0.1-10% SiO₂, and 1-3% TiO₂. Other inorganic compounds may bepresent in the bauxite first coating including, but not limited to,P₂O₅, MnO, MgO, CaO, etc. These compounds are generally present in lessthan 5% or even 0% relative to the total weight % of the bauxite.

Bentonite is an absorbent aluminum phyllosilicate, impure clayconsisting primarily of montmorillonite. Phyllosilicates are sheetsilicate minerals formed by parallel sheets of silicate tetrahedra withSi₂O₅ or a 2:5 ratio, they may be hydrated with either water or hydroxylgroups attached. Montmorillonite generally comprises sodium, calcium,aluminum, magnesium and silicon and oxides and hydrates thereof. Othercompounds may also be present in the bentonite of the present disclosureincluding, but not limited to, potassium-containing compounds and/oriron-containing compounds. There are different types of bentonite, namedfor the respective dominant element, such as potassium (K), sodium (Na),calcium (Ca), and aluminum (Al). For industrial purposes, two mainclasses of bentonite exist: sodium and calcium bentonite. Therefore, interms of the present disclosure bentonite may refer to potassiumbentonite, sodium bentonite, calcium bentonite, aluminum bentonite, andmixtures thereof, depending on the relative amounts of potassium,sodium, calcium, and/or aluminum in the bentonite first coating.

Dolomite is an anhydrous carbonate mineral composed of calcium magnesiumcarbonate, e.g., CaMg(CO₃)₂. Dolomite can also describe the sedimentarycarbonate rock composed primarily of mineral dolomite, known asdolostone or dolomitic limestone. The mineral dolomite crystallizes inthe trigonal-rhombohedral system and forms white, tan gray or pinkcrystals. Dolomite is a double carbonate, having an alternatingstructural arrangement of calcium and magnesium ions. In one embodiment,the first coating comprises dolomite and the dolomite first coatingcomprises 15-25% Ca, 10-20% Mg, 10-20% C, and 40-60% O, with the calciumand magnesium being present primarily as oxides or hydroxides. Otherinorganic compounds may be present in the dolomite first coatingincluding, but not limited to, Al₂O₃, MnO, Fe₂O₃, etc. These compoundsare generally present in less than 5% or even 0% relative to the totalweight % of the dolomite.

It is envisioned that other types of sedimentary rock sources may beused in lieu of bauxite, bentonite, and/or dolomite as material in thefirst coating including, but not limited to, limestone, calcite,vaterite, aragonite, magnesite, taconite, gypsum, quartz, marble,hematite, limonite, magnetite, andesite, serpentinite, garnet, basalt,dacite, nesosilicates or orthosilicates, sorosilicates, cyclosilicates,inosilicates, phyllosilicates, tectosilicates, and the like.

“Coating,” “coat,” or “coated” as used herein, refers to a covering thatis applied to a surface of the iron ore core or a coated iron ore core.The coating may “substantially cover” the surface, whereby the % surfacearea coverage of the surface being coated is at least 75%, at least 80%,at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, atleast 98%, at least 99%. In some cases, the coating may “incompletelycover,” or only cover portions of the surface being coated, whereby the% surface area coverage of the surface being coated is less than 75%,less than 65%, less than 60%, less than 55%, less than 50%, less than45%, less than 40%, less than 355, less than 30%, less than 25%, lessthan 20%, less than 15%, less than 10%. The “coating” or “coat” mayrefer to one material (i.e., dolomite, bauxite, bentonite, electric arcfurnace dust, etc.) that covers a surface being coated, oralternatively, the coating may refer to a plurality of materials (i.e.,mixtures) that cover a surface being coated. The plurality of materialsmay be applied to a surface as a mixture or sequential applications ofthe individual materials. With sequential applications of individualmaterials, it may be possible to form distinct layers. These distinctlayers may have a defined interface. The coating thickness of thepresent disclosure may be varied depending on the coating materials andthe process for applying the coating. The term “coating” may also referto a single application of a material, or a plurality of applications ofthe same material.

In one embodiment, the first coating substantially covers the iron orecore, where the first coating covers greater than 75%, preferablygreater than 85%, preferably greater than 90%, preferably greater than95% of the surface of the iron ore core. Alternatively, the firstcoating may be applied to only a portion of the surface of the iron orecore (i.e., incompletely cover), and the applied coating may stillprevent agglomeration. This first coating may be sufficient to preventagglomeration of the iron ore pellets.

In one embodiment, the iron ore pellets have a wt. % of the firstcoating ranging from 0.05-2%, preferably 0.1-1.5%, more preferably0.2%-1.0% relative to the total weight of the iron ore pellets.

In one embodiment, an average thickness of the first coating is 50-150μm, preferably 60-100 μm, more preferably 70-80 μm. In one embodiment,the first coating is uniform. Alternatively, the first coating may benon-uniform. The term “uniform” refers to an average coating thicknessthat differs by no more than 50%, by no more than 25%, by no more than10%, by no more than 5%, by no more than 4%, by no more than 3%, by nomore than 2%, by no more than 1% at any given location on the surface ofthe coated material. The term “non-uniform” refers to an average coatingthickness that differs by more than 5% at any given location on thesurface of the coated material.

The iron ore pellets of the present disclosure further include a secondcoating comprising the coating composition described herein in any ofits embodiments comprising electric arc furnace (EAF) dust in an amountof at least 90% based on the total dry weight of the second coating,preferably at least 95%, preferably at least 97%, preferably at least98%, preferably at least 99%. In a preferred embodiment, the firstcoating is disposed between a surface of the iron ore core and thesecond coating.

In one embodiment, the second coating substantially covers the firstcoating. In this scenario, the second coating covers at least 75%, atleast 80%, at least 85%, at least 90%, at least 95%, at least 96%, atleast 97%, at least 98%, at least 99% of the surface of the firstcoating. Alternatively, the second coating may be applied to only aportion of the surface of the first coating (i.e., incompletely coverthe first coating). In the scenario where the first coating incompletelycovers the iron ore core, the second coating may cover the iron ore corerather than, or in addition to covering the first coating. In oneembodiment, the iron ore pellets have a wt. % of the second coatingranging from 0.05-2%, preferably 0.1-1.5%, more preferably 0.2-1.0%relative to the total weight of the iron ore pellets. In one embodiment,an average thickness of the second coating is 50-150 μm, preferably60-100 μm, more preferably 70-80 μm. Similar to the coverage of thefirst coating, the second coating may cover the first coating and/or theiron ore core in a uniform fashion, or alternatively in a non-uniformfashion.

In a preferred embodiment, the first and second coatings form distinctlayers with distinct and identifiable interfaces between the two layers.In one embodiment, the first and second coatings form distinct layers,although the interface between the two layers is a mixture of both thefirst and second layer. For example, in one embodiment the first layercontains at least one of bauxite, bentonite, and dolomite, and thesecond layer contains electric arc furnace dust. Preferably the majorcomponent of the first layer is not present in the second layer and themajor component of the second layer is not present in the first layer.In one embodiment the iron ore pellets of the present disclosure have aporosity of 1-35%, preferably 5-30%, more preferably 10-25%.

The average thickness of both coatings (the first coating and the secondcoating) on the iron ore core is about 100-300 μm, preferably 120-200μm, more preferably 140-160 μm. Further, the total weight percent of thesum of the first coating and second coating is 0.1-4%, 0.2-3.5%,preferably 0.3-3%, preferably 0.4-2.5%, more preferably 0.5-2% relativeto the total weight of the iron ore pellets. The iron ore pellets mayhave an average pellet diameter of 5-20 mm, preferably 7-18 mm, morepreferably 9-16 mm.

In one embodiment, the first and second coating reduce the formation ofagglomerated iron ore pellets at temperatures in the range of 20° C. to1100° C., preferably 500° C. to 1000° C., preferably 750° C. to 950° C.,preferably 800° C. to 900° C. compared to a substantially similar ironore pellet or iron ore core without the first coating, the secondcoating, or both.

In one embodiment, the iron ore pellets have a % agglomeration of lessthan 5%, preferably less than 4%, preferably less than 3%, preferablyless than 2%, preferably less than 1% in terms of the wt. % ofagglomerated iron ore pellets with a longest length of at least 25 mmrelative to the total weight of the iron ore pellets.

In one embodiment, the thickness of the first and second coatingdecreases by no more than 60%, by no more than 50%, by no more than 40%,by no more than 30%, by no more than 20%, by no more than 10% afterrotating the iron ore pellets at 10-30 rpm, in terms of the averagecoating thickness of the sum of the first and second coating [ASTME376—incorporated herein by reference in its entirety].

According to a third aspect, the present disclosure relates to a processfor manufacturing the iron ore pellets of the present disclosure, in oneor more of their embodiments, including applying at least one selectedfrom the group consisting of bauxite, bentonite, and dolomite to an ironore core to form a coated iron ore core coated with a first coating. Inone embodiment, the applying involves coating the iron ore core with afirst coating, where the first coating covers greater than 75%,preferably greater than 85%, preferably greater than 90%, preferablygreater than 95% of the surface of the iron ore core.

In one embodiment, the first coating is applied to the iron ore core asa slurry, preferably aqueous, comprising 10-30 wt. %, preferably 15-25wt. %, more preferably 18-22 wt. % of bauxite, bentonite and/or dolomiterelative to the total weight of the slurry. “Slurry” as used hereinrefers to a semiliquid mixture typically of particles or particulates ofthe coating material suspended in liquid. The liquid used in the slurryis not envisioned as particularly limiting and is preferably water. Inone embodiment, the slurry has a pH of 4-8, although the pH of theslurry may be more acidic or more basic depending on the application.The slurry may also refer to a suspension, a dispersion, or an emulsion,etc.

The slurry preferably comprises a solids concentration of no more than15 kg of coating material per ton of iron ore pellets to be coated,preferably no more than 10 kg/ton, preferably no more than 5 kg/ton,preferably no more than 4 kg/ton, preferably no more than 3 kg/ton,preferably no more 2 kg/ton, preferably no more than 1 kg/ton,preferably no more than 0.5 kg/ton, preferably no more than 0.25 kg/ton.

In one embodiment, the slurry may further comprise binder materialsincluding, but not limited to, clay materials, cement materials,concrete materials, acrylic polymers or copolymers, polymers orcopolymers of vinyl acetate or synthetic oils which can harden on theparticles holding the coating mixture in place on the surface.

Several methods may be used to coat the iron ore core including, but notlimited to, spray coating, dip coating, brush coating and spin coating.Spray coating is a process whereby the slurry is applied through the airto a surface as atomized particles using a spray coating device. A spraycoating device may employ compressed gas, such as air, to atomize anddirect the slurry.

Dip coating is a process whereby the pellet is inserted and removed froma bath of the slurry. The pellet is immersed in the slurry and thecoating deposits itself on the pellet while being removed from the bath.The excess liquid can be drained from the pellet during this process,and the liquid of the slurry can then be evaporated.

Brush coating is a process whereby a slurry is smoothed on the surfaceby a brush or by multiple brushes. Spin coating is a process whereby aslurry is applied to the center of the pellet and the pellet is thenrotated at high speed to spread the coating material by centrifugalforce.

It is envisaged that the coating may be applied manually or throughautomation and that the applications of coatings may be done toindividual iron ore cores or coated iron ore cores or in parallel to aplurality of iron ore cores or coated iron ore cores at the same time.

In one embodiment, the process for manufacturing the iron ore pelletsalso includes measuring a surface area coverage of the first coating onthe iron ore core. In one embodiment, the surface area coverage ismeasured with at least one instrument selected from the group consistingof an optical microscope, an X-ray diffractometer, an X-ray fluorescencespectrometer, and a scanning electron microscope. Further, the surfacearea coverage may be measured upon visual inspection.

In addition to measuring the surface area coverage, other coatingcharacteristics may be measured to determine if an acceptable amount ofcoating has been applied. For instance, the thickness of the coating canbe measured using one or more of these techniques. Further, themeasuring may involve an analysis of the porosity and/or surfaceroughness of the coating surface, for instance by measuring a specificsurface area (i.e., BET surface area) through BET adsorption or gaspermeability techniques.

In a preferred embodiment, the process further comprises drying thecoated iron ore core for 0.5-24 hours, preferably 0.5-12 hours, morepreferably 1-8 hours, even more preferably 1-6 hours prior to applyingthe second coating. By drying the first coating prior to applying thesecond coating, the formation of two distinct coating layers may beobtained. The formation of two distinct layers may be advantageous toprevent pellet agglomeration and to prevent premature removal of thecoatings prior to an iron reduction process.

Further, the process of applying the first coating and measuring thecoating characteristics (i.e., surface area coverage, thickness, etc.)can be repeated a plurality of times in an iterative fashion until anacceptable level of coating is achieved (e.g., greater than 75% surfacearea coverage of the iron ore core).

The process for manufacturing the iron ore pellets also involvesapplying the coating composition comprising electric arc furnace (EAF)dust described herein in any of its embodiments to the coated iron orecore to form the iron ore pellets coated with the first coating and thesecond coating. In one embodiment, the applying involves coating thecoated iron ore core with the second coating, where the second coatingcovers greater than 50%, preferably greater than 60%, preferably greaterthan 70%, preferably greater than 75%, preferably greater than 85%,preferably greater than 90%, preferably greater than 95% of the surfaceof the coated iron ore core.

In one embodiment, the second coating is applied to the iron ore corecoated with a first coating as a slurry comprising 10-30 wt. %,preferably 15-25 wt. %, more preferably 18-22 wt. % of EAF dust relativeto the total weight of the slurry. The second coating may be appliedusing the techniques used to apply the first coating (e.g., spraycoating, dip coating, brush coating and spin coating).

The slurry preferably comprises a solids concentration of no more than15 kg of EAF dust coating composition per ton of iron ore pellets to becoated, preferably no more than 10 kg/ton, preferably no more than 5kg/ton, preferably no more than 4 kg/ton, preferably no more than 3kg/ton, preferably no more 2 kg/ton, preferably no more than 1 kg/ton,preferably no more than 0.5 kg/ton, preferably no more than 0.25 kg/ton,most preferably 5-0.25 kg/ton.

In another embodiment, the process for manufacturing the iron orepellets also includes measuring a surface area coverage of the secondcoating on the first coating. The second coating surface area coverageand coating characteristics can be measured using methods of analysisused to measure the first coating.

Further, the process may also include drying the second coating, andrepeating the application of the second coating a plurality of times inan iterative fashion until an acceptable level of coating is achieved(e.g., greater than 75% surface area coverage of the coated iron orecore).

In a preferred embodiment, the process for manufacturing the iron orepellets of the present disclosure in any of their embodiments furthercomprises determining a clustering index and/or performing a reductionunder load test in accordance with international standard [ISO11256—incorporated herein by reference in its entirety] to evaluate thequality of the iron ore pellets as a feedstock for a direct reductionprocess. ISO 11256 specifies a method to provide a relative measure forevaluating the formation of cluster of iron ore pellets when reducedunder conditions resembling those prevailing in shaft direct reductionprocesses.

A schematic diagram of an exemplary reduction under load (ISO 11256)apparatus is shown in FIG. 1. In a preferred embodiment, the apparatuscomprises a reduction tube, a loading device, waste gas, a furnace, anda gas supply system. The reduction tube comprises an outer reductiontube 1, an inner reduction tube 2, upper and lower perforated platescomprising a test portion 3, a gas inlet 4, a gas outlet 5, and athermocouple exit 6. The loading device comprises a compressed air inlet7, a pressure cylinder 8, a frame for the pressure cylinder 9, and aloading ram 10. The waste gas comprises a throttle valve 11 and a wastegas fan 12. The gas supply system comprises gas cylinders 15, gasflowmeters 16, and a mixing vessel 17.

In a preferred embodiment, the apparatus is constituted of a verticaloven divided into five heating zones starting from the bottom. Onethermocouple is placed in the oven and a triple thermocouple is placedinside the reaction tube. Reducing gas and nitrogen flow rate iscontrolled by a mass flow meter and controller. The vertical electricaloven is equipped with a weighing system. In a preferred embodiment, Thesystem is capable of applying a total static load of up to 150 kPa on abed of the test portion. The test portion is a 500-2500 g sample ofpellets. The test portion comprises 50% pellets having a size in therange 20-12.5 mm and 50% having a size in the range of 12.5-5 mm. Thepellet sample is isothermally reduced in a fixed bed at 700-1100° C.,preferably 750-1000° C., preferably 800-900° C., or 850° C. under staticload using a reducing gas consisting of 30% CO, 15% CO₂, 45% H₂, and 10%N₂ in a flow rate of 30-50 L/min, preferably 40 L/min until a degree ofreduction of 95% was achieved.

In a preferred embodiment, the reduced test portion (cluster) isdisaggregated by tumbling, using a specific tumbling drum. Thepercentage of clusters is determined on the cooled sample. The clusteredpellets consisting of more than two pellets are applied to the tumblertest. A schematic diagram of an exemplary tumble drum apparatus is shownin FIG. 2A (front view) and FIG. 2B (side view). It comprises arevolution counter 18, a door with handle 19, a stub axle 20 with nothrough shaft, two lifters 21 (generally 50 mm×50 mm×5 mm), a directionof rotation 22, and a plate 23.

In a preferred embodiment, the tendency for cluster formation oragglomeration will decrease by increasing the coating amount in kg perton of iron ore core or iron ore pellet. In a preferred embodiment theiron ore pellets have a coating index measurement that achieves theMidrex process standard requirement. As used herein, this means thecluster mass comprising agglomerates of more than one pellet with alongest length of greater than 25 mm after ten revolutions was zero or0%. This confirms that the utilization of the coating compositiondescribed herein in any of its embodiments as a secondary coatingmaterial for iron ore pellets is highly effective in reducing theformation of clusters in the iron ore feed for a reduction furnace. Anexemplary determination of clustering index is further detailed below.

According to a fourth aspect, the present disclosure relates to aprocess for manufacturing reduced iron pellets involving i) applying atleast one selected from the group consisting of bauxite, bentonite, anddolomite to an iron ore core to form a coated iron ore core coated witha first coating, ii) applying the coating composition comprisingelectric arc furnace (EAF) dust described herein in any of itsembodiments to the coated iron ore core to form the iron ore pelletscoated with the first coating and the second coating, iii) feeding thecoated iron ore pellets into a reduction furnace, and iv) reducing theiron ore pellets with a reducing gas to form reduced iron pellets. Thetechniques used to apply the first and second coating, as well as themeasurement techniques used to analyze the coating characteristics ofthe applied coatings have been mentioned previously.

In one embodiment, the process further comprises drying the coated ironore core for 0.5-24 hours, preferably 0.5-12 hours, more preferably 1-8hours, even more preferably 1-6 hours prior to applying the secondcoating. By drying the first coating prior to applying the secondcoating, the formation of two distinct coating layers may be obtained.The formation of two distinct layers may be advantageous to preventpellet agglomeration and to prevent premature removal of the coatingsprior to an iron reduction process.

In one embodiment, the temperature for the reduction is up to 1100° C.,preferably up to 1000° C., more preferably up to 950° C. The reducingmay be performed isothermally, or alternatively, a temperature gradientmay be used to reduce the iron ore throughout the reduction process. Inone embodiment, the reducing gas is hydrogen (H₂). In one embodiment,the reducing gas is carbon monoxide (CO). In a preferred embodiment, thereducing gas comprises both hydrogen and carbon monoxide. In thisscenario, other gases may be present in the reducing gas, includingcarbon dioxide, nitrogen and the like. The ratio of hydrogen to carbonmonoxide may be about 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1,1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10. The reducing gas of thepresent disclosure may be derived from natural gas, coal or both.

In one embodiment, the iron ore pellets are reduced in a directreduction apparatus. In one embodiment, the direct reduction apparatusis a fixed-bed reactor. Alternatively, in one embodiment, the directreduction apparatus is a moving-bed shaft. In a preferred embodiment,the direct reduction apparatus is a vertical moving-bed shaft. In avertical moving-bed shaft apparatus, the iron ore pellets, in one ormore of their embodiments, are placed proximal to the top of themoving-bed shaft, where the iron ore pellets are heated and allowed tomove towards the bottom of the moving-bed shaft gradually as they arereduced. The reducing gas is flowed countercurrent to the movement andfeeding of the iron ore pellets. Then the reduced iron pellets arecollected proximal to the bottom of the shaft apparatus. In a verticalmoving-bed shaft reduction apparatus, the avoidance of agglomerated ironore pellets is essential to allow the downward movement of the iron orepellets for reduction and to allow for efficient flow of the reducinggas upwardly. Therefore, the first and second coating of the iron orepellets may provide a more efficient direct reduction process byminimizing the formation of agglomerates. The wt. % of iron in thereduced iron pellets is greater than 90%, greater than 91%, greater than92%, greater than 93%, greater than 94%, greater than 95%, relative tothe total weight of the reduced iron pellet.

In one embodiment, the process further comprises tumbling the iron orepellets and/or the reduced iron pellets and weighting agglomerated ironore pellets and/or reduced iron pellets with a longest length of atleast 25 mm relative to the total weight of the iron ore pellets and/orthe reduced iron pellets to determine % agglomeration.

It is envisaged that the reduced iron pellets of the present disclosuremay be used for the manufacture of steel and steel related products. Thetype of steel produced using the reduced iron pellets of the presentdisclosure may vary depending on added alloying elements. Steel is analloy of iron and carbon that is widely used in construction and otherapplications because of its high tensile strength and low cost. Carbon,other elements, and inclusions within iron act as hardening agents thatprevent the movement of dislocations that naturally exist in the ironatom crystal lattices. The carbon in typical steel alloys may contributeup to 2.1% of its weight. The steel material of the present disclosuremay be any of the broadly categorized steel compositions, includingcarbon steels, alloy steels, stainless steels and tool steels. Carbonsteels contain trace amounts of alloying elements and account for 90% oftotal steel production. Carbon steels can be further categorized intothree groups depending on their carbon content: low carbon steels/mildsteels contain up to 0.3% carbon, medium carbon steels contain 0.3-0.6%carbon, and high carbon steels contain more than 0.6% carbon. Alloysteels contain alloying elements (e.g., manganese, silicon, nickel,titanium, copper, chromium, and/or aluminum) in varying proportions inorder to manipulate the steel's properties, such as its hardenability,corrosion resistance, strength, formability, weldability, or ductility.Stainless steels generally contain between 10-20 wt. % chromium as themain alloying element and are valued for high corrosion resistance. Withover 11 wt. % chromium, steel is about 200 times more resistant tocorrosion than mild steel. These steels can be divided into three groupsbased on their crystalline structure: austenitic steels; ferriticsteels; and martensitic steels. Tool steels contain tungsten,molybdenum, cobalt and vanadium in varying quantities to increase heatresistance and durability, making them ideal for cutting and drillingequipment.

In one embodiment, the reduced iron pellets manufactured by the directreduction process are maintained at or near the temperature used duringthe reducing, and are transferred at this elevated temperature to asteelmaking apparatus (e.g., blast furnace, etc.), such that less heatis required to melt the reduced iron pellets during a steelmakingprocess.

The examples below are intended to further illustrate protocols forpreparing and assessing the coated iron ore pellets and reduced ironpellets described herein, and are not intended to limit the scope of theclaims.

Example 1 Raw Materials

SAMARCO iron ore pellets were used in the experiments. This ore ispractically used in iron making processes in the Saudi Iron and SteelCompany (HADEED). Electric arc furnace (EAF) dust (lime dust) generatedfrom an electric arc furnace during charging of dolo-lime, lump lime,and special lime for slag formation was used. The iron ore and EAF dustwere characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF),and scanning electron microscopy (SEM).

The various characterization tests of the iron ore pellets showed thatiron oxide (Fe₂O₃) is the major phase with the presence of SiO₂, CaO,and Al₂O₃ as minor components (FIG. 3 and Table 1).

TABLE 1 X-ray fluorescence (XRF) chemical analysis of SAMARCO iron orepellets COMPOUNDS Conc. % Elements Conc. % O 30.8850 Na₂O 0.1100 Na0.0835 MgO 0.1350 Mg 0.0815 Al₂O₃ 0.3000 Al 0.1615 SiO₂ 1.8150 Si 0.8484P₂O₅ 0.0710 P 0.0315 K₂O 0.0082 K 0.0069 CaO 0.7810 Ca 0.5655 TiO₂0.0345 Ti 0.0210 V₂O₅ 0.0040 V 0.0023 Cr₂O₃ 0.0328 Cr 0.0226 MnO 0.0554Mn 0.0436 Fe₂O₃ Balance Fe Balance NiO 0.1040 Ni 0.0827

The SEM photos for SAMARCO iron ore samples are shown in FIG. 4A andFIG. 4B. It was observed that grain coalescence with very low microporesand many macropores took place in a dense structure.

The characterization of EAF dust was also performed and is given inTable 2. The EAF dust is mainly Fe₂O₃ (53.09%) with CaO and CaCO₃(39.13%). The morphological examination under SEM with EDX analysis, asgiven in FIG. 5 and FIG. 6, show the average grain size of EAF dust as2.0-10.0 μm while visual observation of the EAF dust indicates that itcontains some coarse grains in the range of 1.0-9.0 mm.

TABLE 2 Chemical analysis for electric arc furnace (EAF) dust PARAMETERMETHOD RESULT UNIT Aluminum as Al₂O₃ Acid Digestion/ICP 0.29 % Antimony(Sb) Acid Digestion/ICP - MS <0.001 % Arsenic (As) Acid Digestion/ICP -MS <0.001 % Barium (Ba) Acid Digestion/ICP 0.041 % Boron (B) AcidDigestion/ICP 0.014 % Chromium (Cr) Acid Digestion/ICP - MS <0.001 %Copper (Cu) Acid Digestion/ICP - MS 0.0017 % Lead (Pb) AcidDigestion/ICP - MS <0.001 % Manganese (Mn) Acid Digestion/ICP 0.48 %Mercury (Hg) Acid Digestion/ICP - MS <0.001 % Nickel (Ni) AcidDigestion/ICP - MS 0.0011 % Selenium (Se) Acid Digestion/ICP - MS 0.0056% Silver (Ag) Acid Digestion/ICP - MS <0.001 % Zinc (Zn) AcidDigestion/ICP - MS 0.0085 % Molybdenum (Mo) Acid Digestion/ICP - MS<0.001 % Thorium (Th) Acid Digestion/ICP - MS <0.001 % Uranium (U) AcidDigestion/ICP - MS <0.001 % Vanadium (V) Acid Digestion/ICP - MS 0.0127% Strontium (Sr) Acid Digestion/ICP 0.004 % Cadmium (Cd) AcidDigestion/ICP - MS <0.001 % Silica as SiO₂ Gravimetry 3.02 % Lithium(Li) Acid Digestion/ICP <0.001 % Iron Oxide as Fe2O3 Acid Digestion/ICP53.09 % Calcium Oxide Acid Digestion/ICP 14.03 % Magnesium Oxide AcidDigestion/ICP 3.47 % Sulphate Water Extraction/IC 0.06 % Chloride WaterExtraction/IC 0.05 % Sodium Water Extraction/IC 0.09 % Potassium WaterExtraction/IC 0.04 % Carbonate as CaCO3 Volumetry 25.1 % Moisture ASTM D2974 0.05 % Carbon Content ASTM D 2974 0.18 % LOI @ 550° C. ASTM D 29740.38 % LOI @ 800° C. ASTM D 2974 0.64 %

Example 2 Coating of Iron Ore Pellets and Adhesive Characterization

SAMARCO iron ore pellets were coated comparatively with variousconcentrations of cement and electric arc furnace (EAF) dustsuspensions. 5000 g of SAMARCO iron ore pellets were used in eachcoating test. Pellets were placed in a disc pelletizer of 50 cm indiameter rotating at 20 rpm. The coating was applied by spraying asuspension of coating material (cement or EAF dust). Solidconcentrations (2.0 Kg cement or EAF dust per ton of iron ore) using 20%suspension concentration were applied.

Coated pellets were left to air-dry for 4 hrs followed by rotation ofthe pellets in a disc pelletizer for 10 min at a predetermined speed (20rpm) and angle to cause rubbing of the pellets against each other andremoval of the loose and/or un-adhered particles. The remaining coatingand its uniformity on the surface of the pellets was evaluated under amicroscope at standard magnification. The coating index of the particlesis expressed as the percentage of the remaining coating thickness afterthe rubbing test: Coating Index=(T₂/T₁)×100, wherein T₁=coatingthickness before the rotation test and T₂=coating thickness after therotation test.

For EAF dust coated pellets, SAMARCO pellets before and after the EAFdust coating and after the rubbing test were visually inspected. Thesurface and internal layers of the coated pellets before and afterrubbing were analyzed by energy-dispersive X-ray spectroscopy (EDX) asshown in FIG. 8 and FIG. 10 respectively. It was found that calcium andcarbon have a higher percentage on the surface layer compared to theinternal core confirming the formation of a coating layer comprisinglime (FIG. 8). Also, after the rubbing test a higher percentage of Caand C are observed on the surface layer compared to the internal core toconfirm the presence of the coating layer after rubbing. The residualpowder of the EAF dust coating layer after rotation for 10 min in thedisc pelletizer is less than 0.1 g.

Comparatively similar results were observed in the case of cementcoating. SAMARCO pellets before and after the cement coating and afterthe rubbing test were visually inspected. The surface and internallayers of the coated pellets before and after rubbing were analyzed byEDX as shown in FIG. 12 and FIG. 14, respectively. It was found thatcalcium, aluminum, and silicon have a higher percentage on the surfacelayer compared to the internal one confirming the formation of a cementcoating layer (FIG. 14). Also, after the rubbing test a higherpercentage of Ca, Al, and Si are observed on the surface layer comparedto the internal one confirming the presence of the coating layer afterrubbing. The residual powder of the cement coating layer after rotationfor 10 min in the disc pelletizer is less than 0.1 g.

Thus, the comparative results of the adhesive characterization reflectedthat EAF dust has relatively acceptable adhesive nature to be used as acoating material for iron ore pellets during production of directreduced iron (DRI).

Example 3 Determination of the Clustering Index (Reduction Under LoadTest)—ISO 11256

ISO 11256 specifies a method to provide a relative measure forevaluating the formation of clusters of iron ore pellets when reducedunder conditions resembling those prevailing in shaft direct-reductionprocesses.

The clustering or sticking index was measured for SAMARCO iron orepellets coated with various concentrations of electric arc furnace (EAF)dust slurry. A schematic diagram of the reduction under load (ISO 11256)apparatus is shown in FIG. 1. The apparatus comprises a reduction tube,a loading device, waste gas, a furnace, and a gas supply system. Thereduction tube comprises an outer reduction tube 1, an inner reductiontube 2, upper and lower perforated plates comprising a test portion 3, agas inlet 4, a gas outlet 5, and a thermocouple exit 6. The loadingdevice comprises a compressed air inlet 7, a pressure cylinder 8, aframe for the pressure cylinder 9, and a loading ram 10. The waste gascomprises a throttle valve 11 and a waste gas fan 12. The gas supplysystem comprises gas cylinders 15, gas flowmeters 16, and a mixingvessel 17.

The apparatus is constituted of a vertical oven divided into fiveheating zones starting from the bottom. One thermocouple is placed inthe oven and a triple thermocouple is placed inside the reaction tube.Reducing gas and nitrogen flow rate is controlled by a mass flow meterand controller. The vertical electrical oven is equipped with a weighingsystem.

The system is capable of applying a total static load of 147 kPa on abed of the test portion. The test portion is a 2000 g sample of pellets.The test portion comprises 50% pellets having a size in the range16.0-12.5 mm and 50% having a size in the range of 12.5-10 mm. Thepellet sample is isothermally reduced in a fixed bed at 850° C. understatic load using a reducing gas consisting of 30% CO, 15% CO₂, 45% H₂and 10% N₂ in a flow rate of 40 L/min until a degree of reduction of 95%was achieved.

The reduced test portion (cluster) is disaggregated by tumbling, using aspecific tumbling drum. The percentage of clusters is determined on thecooled sample. The clustered pellets containing more than two pelletsare applied to the tumbler test. A schematic diagram of the tumble drumapparatus is shown in FIG. 2A (front view) and FIG. 2B (side view). Itcomprises a revolution counter 18, a door with handle 19, a stub axle 20with no through shaft, two lifters 21 (50 mm×50 mm×5 mm), a direction ofrotation 22, and a plate 23.

The tumble drum is made of a steel plate at least 5 mm in thickness,having an internal diameter of 1000 mm and an internal length of 500 mm.Two equally spaced L-shaped steel lifters, 50 mm flat by 50 mm high by 5mm thick and 500 mm long are solidly attached longitudinally inside thedrum by welding, so as to prevent accumulation of material between thelifter and drum. Each lifter is fastened so that it points towards theaxis of the drum, with its attached leg pointing away from the directionof rotation, thus providing a clear unobstructed shelf for lifting theiron ore pellets sample. The door is constructed so as to fit into thedrum forming a smooth inner surface. During the test, the door isrigidly fastened and sealed to prevent any loss of sample. The drum isrotated on stub axles attached to its ends by flanges welded to providesmooth inner surfaces. The drum is replaced when the thickness of theplate is reduced to 3 mm in any area. The lifters are replaced when theheight of the shelf is reduced to less than 47 mm.

All material is removed from the reduction tube. The mass of the reducedmaterial is determined (m_(r)). During this operation, some individualpellets usually separate from the clustered material. These pellets areremoved and the mass of the clustered material is recorded (m_(e), 1).This step is considered as the first disaggregation operation. Theremoval of the test portion from the reduction tube is a critical stepand care must be taken to avoid its untimely disaggregation. Theclustered material is placed inside the tumble drum and rotated for atotal of 35 revolutions, divided into 7 disaggregation operations of 5revolutions each. After each disaggregation operation, the mass of theremaining clusters is measured and recorded as a series (m_(c), 2,m_(c), 3 . . . m_(c), 8). Any individual pellets that are separated fromthe clustered material shall be removed prior to the next disaggregationoperation.

The clustering index (CI) is expressed as a percentage and is calculatedfrom the following equation where m_(r) is the total mass, in grams, ofthe test portion after reduction and m_(c), i is the mass, in grams, ofthe clusters after the i^(th) disaggregation operation expressed byformula (II):

$\begin{matrix}{{{C\; I} = {\frac{100}{8 \times m_{r}} \times {\sum\limits_{i = 1}^{8}m_{c}}}},i} & ({II})\end{matrix}$

The clustering index measurement (ISO11256) was applied comparatively onSAMARCO iron ore pellets coated with various electric arc furnace (EAF)dust coating conditions, including 20% EAF slurry concentrations with acoated material amount of 0.5, 2.0 and 4.0 Kg per ton of iron ore. Theresults of the clustering index measurements are show in tables 3, 4 and5.

TABLE 3 Clustering index measurement for SAMARCO iron ore pellets coatedwith 20% electric arc furnace dust slurry concentration and 0.5 Kgelectric arc furnace dust per ton of iron ore pellets No Cluster Mass(g) 1 1114 (after Red.) 2 53 (after 05 rev.) 3 29 (after 10 rev.) 4 12(after 15 rev.) 5 5 (after 20 rev.) 6 5 (after 25 rev.) 7 0 (after 30rev.) 8 0 (after 35 rev.)

TABLE 4 Clustering index measurement for SAMARCO iron ore pellets coatedwith 20% electric arc furnace dust slurry concentration and 2.0 Kgelectric arc furnace dust per ton of iron ore pellets No Cluster Mass(g) 1 900 (after Red.) 2 47 (after 05 rev.) 3 32 (after 10 rev.) 4 21(after 15 rev.) 5 21 (after 20 rev.) 6 21 (after 25 rev.) 7 21 (after 30rev.) 8 18 (after 35 rev.)

TABLE 5 Clustering index measurement for SAMARCO iron ore pellets coatedwith 20% electric arc furnace dust slurry concentration and 4.0 Kgelectric arc furnace dust per ton of iron ore pellets No Cluster Mass(g) 1 583 (after Red.) 2 17 (after 05 rev.) 3 0 (after 10 rev.) 4 0(after 15 rev.) 5 0 (after 20 rev.) 6 0 (after 25 rev.) 7 0 (after 30rev.) 8 0 (after 35 rev.)

It was noticed that the tendency for cluster formation decreased byincreasing the coating amount from 0.5, 2.0 to 4.0 Kg per ton of ironore. Also it was found that the coating index measurement for iron orepellets coated with 20% EAF dust slurry concentrations in 4.0 Kg per tonof iron ore achieved the Midrex process standard requirement. As usedherein, this means the cluster mass comprising agglomerates of more thanone pellet with a longest length of greater than 25 mm after 10revolutions was zero or 0%. These obtained results confirm that theutilization of electric arc furnace (EAF) dust as a coating material foriron ore pellets is highly promising.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, defines, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

1. A coating composition comprising: (a) at least 90 wt. % of electricarc furnace (EAF) dust based on the total dry weight of the coatingcomposition, wherein the electric arc furnace dust comprises greaterthan 40 wt. % of iron (III) oxide (Fe₂O₃) and greater than 30 wt. % ofcalcium oxide (CaO) and calcium carbonate (CaCO₃) combined, based on thetotal dry weight of the electric arc furnace dust; and (b) at least onebinder material selected from a clay material or a cement material orboth.
 2. The coating composition of claim 1, wherein the electric arcfurnace dust comprises at least 20 wt. % CaCO₃ and at least 10 wt. %CaO.
 3. The coating composition of claim 2, wherein the electric arcfurnace dust comprises 45 wt. % to 60 wt. %, preferably 50 wt. % to 55wt. % Fe₂O₃, 20 wt. % to 30 wt. %, preferably 23 wt. % to 27 wt. %CaCO₃, and 10 wt. % to 20 wt. %, preferably 12 wt. % to 17 wt. % CaO. 4.The coating composition of claim 3, wherein the electric arc furnacedust comprises 50 wt. % to 55 wt. % Fe₂O₃, 23 wt. % to 27 wt. % CaCO₃,and 12 wt. % to 17 wt. % CaO.
 5. The coating composition of any one ofclaims 1 to 4, further comprising 0.5-5 wt. % of MgO and 0.5-5 wt. % ofSiO₂ relative to the total dry weight of the coating composition.
 6. Thecoating composition of any one of claims 1 to 4, which is substantiallyfree of zinc, chromium, manganese, lead, nickel, sodium and potassium.7. The coating composition of any one of claims 1 to 4, which issubstantially free of reducing agents comprising ferrous chloride and/orferrous sulfate.
 8. The coating composition of any one of claims 1 to 4,wherein the coating composition is a granular powder having an averageparticle size of 1-20 μm.
 9. Iron ore pellets comprising: an iron orecore; a first coating comprising at least one selected from the groupconsisting of bauxite, bentonite, and dolomite; and a second coatingcomprising the coating composition of any one of claims 1 to 9 in anamount of at least 90% based on the total dry weight of the secondcoating, wherein the first coating is disposed between a surface of theiron ore core and the second coating.
 10. The iron ore pellets of claim9, wherein the average diameter or average longest length of the pelletsranges from 5-20 mm.
 11. The iron ore pellets of claim 9, wherein theiron ore pellets comprise from 0.05-2 wt. % of the first coatingrelative to the total weight of the iron ore pellets and from 0.05-2 wt.% of the second coating relative to the total weight of the iron orepellets.
 12. The iron ore pellets of claim 9, wherein the first coatingcovers greater than 75% of the surface of the iron ore core and thesecond coating covers greater than 75% of the surface of the firstcoating.
 13. The iron ore pellets of claim 9, wherein the averagethickness of the first coating is 50-150 μm and the average thickness ofthe second coating is 50-150 μm.
 14. The iron ore pellets of claim 9,wherein the first and second coating reduce the formation ofagglomerated iron ore pellets at temperatures in the range of 20° C. to1100° C. compared to a substantially similar iron ore pellet without thefirst coating, the second coating, or both coatings.
 15. A process formanufacturing iron ore pellets, the process comprising: applying a firstcoating as a slurry comprising at least one selected from the groupconsisting of bauxite, bentonite, and dolomite in an amount of 10-30 wt.% based on the total weight of the slurry to an iron ore core to form acoated iron ore core coated with a first coating; and applying a secondcoating as a slurry comprising the coating composition of any one ofclaims 1 to 8 in an amount of 10-30 wt. % based on the total weight ofthe slurry to the coated iron ore core to form the iron ore pelletscoated with the first coating and the second coating, wherein the secondcoating is applied as a slurry comprising a solid concentration of0.25-5 kg of the coating composition per ton of coated iron ore cores.16. The process of claim 15, further comprising determining a clusteringindex of the iron ore pellets in accordance with ISO 11256 to evaluatethe quality of the iron ore pellets as a feedstock for a directreduction process.
 17. The process of claim 15, wherein the iron orepellets have a Midrex standard requirement of 0% agglomerated pelletswith a longest length of greater than 25 mm relative to the total weightof iron ore pellets after 10 or fewer tumbling revolutions.
 18. Aprocess for manufacturing reduced iron pellets, the process comprising:applying a first coating comprising at least one selected from the groupconsisting of bauxite, bentonite, or dolomite to an iron ore core toform a coated iron ore core; applying a second coating comprising thecoating composition of any one of claims 1 to 8 to the coated iron orecore to form iron ore pellets; feeding the iron ore pellets into areduction furnace; and reducing the iron ore pellets with a reducing gasat temperatures up to 1100° C. to form reduced iron pellets.
 19. Theprocess of claim 18, wherein the first coating is applied to the ironore core as a slurry comprising 10-30 wt. % of bauxite, bentonite, ordolomite based on the total weight of the slurry, the second coating isapplied to the coated iron ore core as a slurry comprising 10-30 wt. %of the coating composition based on the total weight of the slurry, andwherein the second coating is applied as a slurry comprising a solidconcentration of 0.25-5 kg of the coating composition per ton of ironore pellets to be coated.